Are the ideas in the paper "Governance by Glass-Box: Implementing Transparent Moral Bounds for AI Behaviour" novel?
Poel's paper on Translating Values into Design Requirements articulates a framework for mapping abstract values and norms into concrete design constraints that an engineer could work with. The example used in the paper is mapping beliefs about animal welfare to design constraints on chicken coups. 

The newer paper by Tubella et al. on Governance by Glass-Box builds on Poel's idea (and in fact, cite's Poel several times). It basically suggests that we should use Poel's design process, but that in something like an AI system, we also need to use an "observation phase" to validate the system, because unlike the problem of engineering a chicken coup, an AI system may appear to have met design constraints, but routinely violate them in production. 

So, you're right that the Tubella et al. paper is essentially proposing the combination of Poel's framework for translating values into design constraints with the old idea of black-box testing, but this combination itself appears to be a new, if modest, contribution.